Preparation of copper-based bimetallic catalyst supported on cathode and application in carbon dioxide reduction

Abstract

The application relates to a preparation method of a copper-based bimetallic catalyst-loaded electric cathode and application of the electric cathode in carbon dioxide reduction, and belongs to the technical field of electrode preparation of molecular catalysts. The catalyst is a copper-based bimetallic complex CuCu-salophen, which can stably maintain its molecular structure in a reaction system. Since the molecule has a planar conjugated structure, the molecule can be loaded on the surface of carbon material through a pi-pi stacking effect, so that a stable molecular-carbon-based composite material is constructed; in the electric catalytic carbon dioxide reduction reaction, the molecule exhibits excellent catalytic activity and good selectivity. Compared with a mononuclear copper molecular catalyst, the bimetallic catalyst can control the reaction path, so that the main hydrocarbon product of carbon dioxide reduction is changed from CH4 to C2H4. In addition, the hydrogen evolution side reaction can be further inhibited by enhancing the hydrophobicity of the electrode. Meanwhile, the influence of different groups on the catalytic effect of the catalyst is explored, and it is found that CuCu-salophen-Ph is optimal in the reduction of hydrocarbon products. The catalyst has a good application prospect in the fields of electric catalytic conversion of carbon dioxide, energy storage and conversion.

Description

Technical Field

[0001] This invention pertains to the field of electrocatalysis in the chemical energy sector, and specifically relates to the electrocatalytic reduction of carbon dioxide (CO2RR) to hydrocarbon products such as C2H4 and CH4 using metal complexes. Background Technology

[0002] The multi-electron reduction of CO2 and its highly selective conversion into high-value-added hydrocarbons such as CH4 and C2H4 not only promotes the recycling of carbon resources but also yields key chemical raw materials. Among numerous catalytic systems, molecular catalysts exhibit unique advantages in CO2 reduction reactions due to their clear structure and high tunability. By carefully constructing ligands, the electronic structure, steric environment, and secondary coordination loops of the catalytic center can be adjusted, thereby effectively enhancing catalytic activity and improving product selectivity. Simultaneously, molecular catalysts not only serve as a platform for constructing highly efficient catalytic sites but also, due to their clear structure, become ideal models for exploring reaction mechanisms, helping to reveal the relationship between structure and activity and providing guidance for the rational design of subsequent catalysts.

[0003] In recent years, mononuclear metal complexes have made significant progress as electrocatalysts in CO2 reduction and reduction (CO2RR). However, due to the high energy barrier of multi-electron transfer during deep reduction, the CO2 reduction products of mononuclear molecular catalysts in aqueous electrolytes are mainly low-value-added products such as H2 and CO. To address these shortcomings of mononuclear molecular catalysts, binuclear metal complexes, due to the synergistic effect between metal centers and their more efficient electron transfer capabilities, have gradually become a research hotspot. Binuclear metal complexes exhibit high flexibility, providing multiple sites and high-valence metal centers during electrocatalysis, inhibiting intramolecular ligand degradation caused by multi-electron transfer. Furthermore, the synergistic effect between their binuclear metals makes deep CO2 reduction possible.

[0004] A relatively rich chemical system has been developed around CO2RR. Among them, copper-based catalysts are widely used for the generation of multi-carbon products due to their ability to promote C-C coupling, but they are often limited by high overpotential requirements and insufficient operational stability. Therefore, the development of efficient, stable molecular catalysts with deep CO2 reduction capabilities has gradually become a research hotspot. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned technical problems and provide a method for preparing a copper-based bimetallic molecular catalyst cathode, and to apply it to the electrocatalytic reduction of carbon dioxide. This catalyst can selectively reduce CO2 in KHCO3 aqueous solution to CH4 and C2H4, and exhibits good stability, without the formation of new redox couples during rinsing experiments. This provides a simple strategy for studying cathodes supported on transition metal complexes as highly efficient electrochemical catalysts for CO2 reduction. Furthermore, the Faraday efficiency of H2 production in aqueous systems can be further reduced by adjusting the hydrophobicity of the electrode.

[0006] The molecular catalyst CuCu-salophen has two copper atoms located symmetrically at the molecular center, forming a Cu···Cu binuclear site, bridged by two oxygen atoms (O). Each Cu atom is also coordinated with surrounding N atoms, exhibiting an overall rigid, aromatically fused binuclear sandwich ligand that fixes the two Cu atoms within the same molecular framework. This structure, to a certain extent, ensures the stability of the molecular catalyst during electrolysis. The polybenzene ring structure in the ligand also contributes to the loading of the molecular catalyst with carbon black.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing a binuclear copper-based molecular catalyst includes the following steps:

[0009] (1) Under stirring conditions, o-phenylenediamine solution was added dropwise to 2-hydroxy-5-methylisophthalaldehyde solution, and the reaction was refluxed under an inert atmosphere to obtain cyclic salophen ligand;

[0010] The molar ratio of 2-hydroxy-5-methylisophthalaldehyde to o-phenylenediamine is 1:1, and both the o-phenylenediamine solution and the 2-hydroxy-5-methylisophthalaldehyde solution are anhydrous methanol solutions.

[0011] (2) The salophen ligand was dissolved in DMF at room temperature, and then copper acetate was added. The reaction was carried out under an inert atmosphere and the solid was collected by vacuum filtration to obtain the binuclear copper-based molecular catalyst CuCu-salophen.

[0012] The molar ratio of the salophen ligand to copper acetate is 1:2 to 1:6.

[0013] A binuclear copper-based molecular catalyst was prepared using the method described above.

[0014] A method for preparing a copper-based bimolecular-carbon-based heterogeneous catalyst, wherein the catalyst is mixed with conductive carbon black at a mass ratio of 1:6 to 6:1; the mixture of catalyst and conductive carbon black is dispersed by ultrasonication; stirred, centrifuged, washed, and dried; and the heterogeneous catalyst is obtained.

[0015] A copper-based bimolecular-carbon-based heterogeneous catalyst, wherein the heterogeneous catalyst is prepared by the above-described preparation method.

[0016] Application of a copper-based bimolecular-carbon-based heterogeneous catalyst, wherein the heterogeneous catalyst is used for electrocatalytic carbon dioxide reduction activity.

[0017] A method for preparing an electrocatalytic carbon dioxide reduction cathode, characterized in that: the above-mentioned heterogeneous material is fully dispersed in an ultrasonic solution, the dispersion is sprayed onto carbon paper fiber, and dried; thus, a cathode of heterogeneous catalyst is obtained.

[0018] An electrocatalytic carbon dioxide reduction cathode is prepared using the method described above.

[0019] Application of an electrocatalytic carbon dioxide reduction cathode, wherein the cathode is used for electrocatalytic carbon dioxide reduction.

[0020] Specifically, the cathode is used as the working electrode, the platinum mesh as the counter electrode, the Ag / AgCl electrode as the reference electrode, and the KHCO3 aqueous solution is used as the electrolyte. The H cell is used as the electrolytic cell, and constant potential electrolysis is performed after CO2 is introduced into the KHCO3 solution.

[0021] The above plan is as follows:

[0022] (1) 3 mmol of 2-hydroxy-5-methylisophthalaldehyde was added to a flask containing 30 mL of anhydrous methanol and stirred for 10 minutes. Simultaneously, 3 mmol of o-phenylenediamine was dissolved in 30 mL of methanol. Then, the o-phenylenediamine solution was added dropwise to the flask under magnetic stirring and refluxed at 80 °C for 4 hours under an Ar atmosphere. After the reaction mixture was allowed to cool naturally to room temperature, the resulting orange precipitate was collected by filtration, washed three times with methanol, and dried overnight under vacuum at 60 °C to obtain the salophen ligand.

[0023] (2) The salophen ligand (1 mmol) obtained above was dissolved in 20 mL DMF at room temperature, followed by the addition of 2 mmol of copper acetate monohydrate, and the reaction was carried out under continuous stirring. Afterwards, the reaction flask was connected to a condenser, purged with Ar gas, and heated to 80 °C in an oil bath. After 4 hours of reaction, the solid was collected by vacuum filtration, washed three times with anhydrous diethyl ether, and finally dried in a vacuum oven. The CuCu-salophen molecular catalyst was obtained, which was dark brown in color.

[0024] (3) The dual-core copper-based molecular catalyst CuCu-salophen prepared by the above method is mixed with carbon black at a mass ratio of 3:1 to obtain CuCu-salophen molecular catalyst-carbon-based material heterogeneous catalyst.

[0025] Optionally, in step (1), the molar ratio of o-phenylenediamine to 2-hydroxy-5-methylisophthalaldehyde is 1:1.

[0026] Optionally, in step (2), the ratio of copper acetate monohydrate to salophen ligand is 2:1 to 6:1.

[0027] Optionally, in step (3), the ratio of CuCu-salophen molecular catalyst to carbon black is 1:6 to 6:1.

[0028] Optionally, in step (3), the pretreatment method of the carbon black is as follows: calcining at 400℃-600℃, cooling to room temperature, transferring the carbon black to a 5wt% HCl aqueous solution and ultrasonic treatment; filtering, washing, and drying.

[0029] This invention also relates to the preparation of copper-based bimolecular-carbon-based heterogeneous catalyst materials, the preparation scheme of which is as follows:

[0030] The synthesized molecular catalyst (6 mg) and carbon black (2 mg) were added sequentially to 1 mL of DMF. Each addition was followed by sonication for 1 h. Subsequently, 50 μL of Nafion solution was added to the mixture, and sonication was continued for 2 h to form a homogeneous dispersion for later use.

[0031] A cathode for electrocatalytic carbon dioxide reduction is prepared using the aforementioned copper-based bimolecular-carbon-based heterogeneous catalyst material.

[0032] Typically, 25 μL of the uniform dispersion is dropped onto a 1×1 cm² plate each time. 2 The hydrophobic carbon fiber paper was coated on both sides, for a total of 4 coats. After each coat, the hydrophobic carbon fiber paper should be dried in an oven for 20 minutes.

[0033] The beneficial effects of this invention are as follows:

[0034] (1) The bimetallic copper-based molecular catalyst CuCu-salophen disclosed in this invention has a significant CC coupling effect compared with the copper-based mononuclear molecular catalyst Cu-salophen. The bimetallic CuCu-salophen catalyst can regulate the reaction pathway and change the main hydrocarbon product of carbon dioxide reduction from CH4 to C2H4.

[0035] (2) A heterogeneous catalytic system was constructed by anchoring the molecular catalyst onto the carbon black support through π-π stacking. Under -1.6 V (vs. RHE) conditions, the catalyst achieved a high catalytic current density for the reaction of C2H4. Electrochemical performance testing and material morphology characterization results showed a significant synergistic coupling between CuCu-salophen and the carbon black substrate, which promoted charge transport at the electrode / electrolyte interface. Using KHCO3 aqueous solution as the electrolyte, the Faradaic efficiency of C2H4 was 32% at -1.6 V (vs. RHE), while the total Faradaic efficiency of hydrocarbon products exceeded 40%.

[0036] (3) The close proximity of the binuclear copper sites provides active sites for the CC coupling generated by C2H4. Each Cu is also coordinated with the surrounding N atoms, forming a rigid, aromatically fused binuclear sandwich ligand that fixes the two Cu atoms in the same molecular framework. This structure ensures the stability of the molecular catalyst during electrolysis to a certain extent. The cyclic benzene ring structure is beneficial to the loading of the molecular catalyst and carbon black to a certain extent.

[0037] (4) By adjusting the content of polytetrafluoroethylene (PTFE) in the electrode, the hydrophobicity of the electrode can be adjusted, thereby further suppressing the hydrogen evolution effect of CuCu-salophen@KB.

[0038] (5) By testing the effect of CuCu-salophen-X on carbon dioxide reduction after different substituent groups, it was initially concluded that some of the power-generating groups can improve the selectivity of the catalyst for CH4 and C2H4 to a certain extent. Attached Figure Description

[0039] Figure 1 (a) Preparation of CuCu-salophen@KB material (b) Schematic diagram of the preparation of CuCu-salophen@KB electrode.

[0040] Figure 2 Scanning electron microscope images and elemental distribution maps of the CuCu-salophen@KB electrode at different scales.

[0041] Figure 3Transmission electron microscopy images of CuCu-salophen@KB at different scales and elemental distribution under dark conditions.

[0042] Figure 4 The molecular structures are CuCu-salophen, CuCu-salophen-NO2, CuCu-salophen-Br, and CuCu-salophen-Ph.

[0043] Figure 5 (a) High-resolution X-ray photoelectron spectra of Cu 2p of CuCu-salophen and CuCu-salophen@KB electrodes; (b) XPS plot of Cu 2p of CuCu-salophen@KB electrode; (c) XPS plot of C 1s of CuCu-salophen@KB electrode.

[0044] Figure 6 The figures are cyclic voltammetry curves before and after electrolysis; (a) shows the homogeneous CuCu-salophen system and (b) shows the heterogeneous CuCu-salophen@KB system.

[0045] Figure 7 (a) LSV curves of CuCu-salophen@KB and Cu-salophen@KB; (b) Faraday efficiency plots of the products of CuCu-salophen@KB and Cu-salophen@KB.

[0046] Figure 8 (a) LSV curves of CuCu-salophen@KB working electrodes with different PTFE contents; (b) Distribution of Faraday efficiencies of each product under different PTFE contents.

[0047] Figure 9 (a) iT curves of CuCu-salophen-Ph at different potentials; (b) Faraday efficiency graphs of all products of CuCu-salophen-Ph at -0.6V, -0.8V, -1.0V, -1.2V, -1.4V, and -1.6V.

[0048] Figure 10 The Nyquist plots and fitted equivalent circuit diagrams of CuCu-salophen@KB and Cu-salophen@KB are shown at an overpotential of 450mV. Detailed Implementation

[0049] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but this does not limit the present invention in any way.

[0050] In the following experiments, the conductive carbon black used was purchased Ketjen black, product number C914875.

[0051] Example 1

[0052] The specific steps for preparing the CuCu-salophen molecular catalyst are as follows:

[0053] (1) First, 3 mmol of 2-hydroxy-5-methylisophthalaldehyde was added to a three-necked flask equipped with a magnetic stir bar, a condenser, and an argon inlet. 30 mL of anhydrous methanol was added, and the mixture was stirred at room temperature for 10 minutes to fully dissolve the aldehyde and ensure a uniform reaction. At the same time, 3 mmol of o-phenylenediamine was dissolved in 30 mL of anhydrous methanol in another beaker and stirred until clear. Then, under magnetic stirring, the o-phenylenediamine solution was slowly added dropwise to the aldehyde solution through a dropping funnel over 20-30 minutes. Argon gas was continuously introduced during the addition and reaction to prevent oxidation. After the addition was completed, the mixed solution was refluxed at 80 °C for 4 hours to promote the Schiff base condensation reaction between the amine and the aldehyde to form a C=N double bond and a macrocyclic structure under high temperature conditions. After the reaction was completed, the mixture was naturally cooled to room temperature, and an orange precipitate gradually formed. The precipitate was then filtered under vacuum using a Buchner funnel and washed three times with cold anhydrous methanol to remove unreacted substances and byproducts. Finally, the obtained solid was placed in a vacuum drying oven and dried overnight at 60 °C to obtain the macrocyclic ligand for the synthesis of CuCu-salophen molecules.

[0054] (2) First, the pre-synthesized and dried purified Salophen-type macrocyclic ligand (1 mmol) was accurately weighed and dissolved in 20 mL of anhydrous N,N-dimethylformamide (DMF). The solution was stirred thoroughly with a magnetic stirrer at room temperature to ensure complete dissolution and a clear, homogeneous ligand solution. Then, Cu(CH3COO)2 (2 mmol, approximately 0.399 g) was added. The reaction system was then heated in an 80 °C oil bath and refluxed for 4 hours. After the reaction was completed, the system was allowed to cool naturally to room temperature, and the product precipitated as a solid. The precipitate was collected by vacuum filtration using a Buchner funnel and washed three times with anhydrous diethyl ether to remove residual DMF and unreacted copper salts. Finally, the obtained solid was placed in a vacuum oven and dried overnight at 60 °C to obtain the target product, CuCu-salophen binuclear copper molecular catalyst, which was a dark brown powder.

[0055] Preparation of CuCu-salophen@KB heterogeneous catalytic material

[0056] 6 mg of the CuCu-salophen molecular catalyst was weighed and added to 1 mL of anhydrous DMF. The solution was placed in a small glass bottle and then ultrasonically treated for 1 hour to ensure thorough dispersion of the catalyst in the solvent. Next, 2 mg of carbon black was added as a conductive additive to improve the conductivity and specific surface area of ​​the electrode material. After adding the carbon black, ultrasonic treatment continued for 1 hour to ensure thorough mixing with the molecular catalyst and the formation of a relatively stable suspension. Then, 50 μL of a 5 wt% Nafion solution was added to the mixture as a binder to enhance the adhesion of the catalyst to the electrode surface and improve ion transport performance. After adding Nafion 117, ultrasonic treatment continued for 2 hours. Through prolonged ultrasonic energy, the solid components (molecular catalyst and carbon black) were uniformly distributed in the DMF medium and thoroughly mixed with Nafion to form a stable and homogeneous catalyst dispersion, yielding the CuCu-salophen@KB heterogeneous catalyst material.

[0057] The pretreatment method for carbon black before use is as follows: calcination at 400℃-600℃, cooling to room temperature, transferring the carbon black to a 5wt% HCl aqueous solution and ultrasonic treatment; filtration, washing, and drying.

[0058] Comparative Example 1

[0059] To verify that CuCu-salophen exhibits higher electrocatalytic activity for carbon dioxide reduction than Cu-salophen, a mononuclear molecular catalyst, Cu-salophen, was synthesized through similar steps as described above.

[0060] In a clean, dry 250 mL three-necked flask, o-phenylenediamine (2.5 mmol, approximately 0.27 g), salicylaldehyde (5 mmol, approximately 0.61 g), and copper acetate (II) (2.5 mmol, approximately 0.499 g) were added, followed by 50 mL of anhydrous methanol as the reaction solvent. The molar ratio of o-phenylenediamine, salicylaldehyde, and copper acetate (II) was 1:2:1. The mixture was refluxed in an oil bath at 80 °C for 3 hours under continuous argon purging. During the reaction, the solution gradually turned dark, and a solid precipitate formed. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and the precipitate was collected by vacuum filtration through a Buchner funnel. The obtained solid was washed three times each with deionized water and anhydrous ethanol to remove unreacted substances, residual acetate, and byproducts. Finally, the product was dried overnight (at least 12 hours) in a vacuum oven at 60 °C to obtain the target product, the Cu-salophen mononuclear copper complex, which was light green in color.

[0061] Comparative Example 1

[0062] To verify the catalytic effects of CuCu-salophen and catalyst molecules modified with different groups thereon, we synthesized CuCu-salophen-ph, CuCu-salophen-ph-NO2, and CuCu-salophen-Br, respectively, following similar steps to those in Example 1 above. The only difference in the synthesis steps was that the p-phenylenediamine in Example 1 was replaced sequentially with 4,5-diaminonaphthalene, 4,5-dinitro-o-phenylenediamine, and 4,5-dibromo-o-phenylenediamine.

[0063] Preparation of Cu-salophen@KB heterogeneous materials

[0064] The preparation method is similar to that of the CuCu-salophen@KB heterogeneous catalytic material, except that the molecular catalyst of CuCu-salophen is replaced with the molecular catalyst of Cu-salophen, and the rest of the steps are exactly the same, finally obtaining the heterogeneous material Cu-salophen@KB.

[0065] Example 2

[0066] Preparation of electrocatalytic cathode materials

[0067] The prepared CuCu-salophen heterogeneous material was sprayed onto 1×1 carbon paper in four separate applications using a spray gun. After each application, the carbon paper was dried in an oven for 20 minutes to prepare the CuCu-salophen@KB working electrode.

[0068] Comparative Example 2

[0069] As a comparison with Example 2, the prepared Cu-salophen heterogeneous material was sprayed onto 1×1 carbon paper in 4 layers using a spray gun. After each spraying, the carbon paper needed to be dried in an oven for 20 minutes to prepare the Cu-salophen@KB working electrode.

[0070] Example 3

[0071] Purchase PTFE-free carbon paper as the electrode substrate, and follow the procedure in Example 2 to spray CuCu-salophen heterogeneous material onto the hydrophilic carbon paper to prepare a hydrophilic cathode working electrode.

[0072] Comparative Example 3

[0073] Cathode working electrodes with different hydrophobic properties were prepared by spraying CuCu-salophen heterogeneous material onto carbon paper with 20%, 40%, and 60% PTFE content, respectively.

[0074] Example 4

[0075] Electrocatalytic carbon dioxide reduction: CO2 electroreduction tests were conducted at room temperature using a CHI 660E electrochemical workstation. The experimental system was a self-made sealed double-chamber H-type electrolytic cell with a three-electrode structure, and the two chambers were separated by a Nafion 117 membrane. The working electrode was the previously prepared reduction cathode; the reference electrode was Ag / AgCl (0.215 V, relative to NHE); and the counter electrode was a 1×1 cm² electrode. 2 A platinum mesh was used. 30 mL of 0.1 M KHCO3 aqueous solution was added to both the cathode and anode electrolytic chambers as electrolytes. Before the test, CO2 was continuously introduced into the cathode chamber for at least 20 min to ensure the solution was fully saturated. During the experiment, the CO2 flow rate was set to 20 sccm using a digital mass flow controller, and the gas flow rate at the electrolytic cell outlet was recorded in real time using a digital flow detector. The gaseous products generated by electrolysis were then introduced into a gas chromatograph (Agilent 8890) for quantitative and component analysis.

[0076] The detection methods for gaseous and liquid phase products during the testing process are as follows.

[0077] Gas chromatography analysis used high-purity Ar as the carrier gas. The instrument was equipped with two types of detectors: FID and TCD. FID was used to determine CO, CH4, and C2H4, while TCD was used to detect H2, O2, and N2. Before formal testing, a calibration curve was established using a mixed standard gas containing H2, O2, N2, CO, CH4, and C2H4 (with CO2 as the equilibrium gas). The linear fitting relationships for each component were as follows: H2: y = 17.15039x; CO: y = 0.780403x; CH4: y = 0.753935x; C2H4: y = 0.37759x. The liquid phase products were analyzed by... 1 Characterization was performed by 1H NMR: 450 μL of electrolyte and 50 μL of heavy water internal standard solution were mixed and added to the NMR tube. The internal standard was 2.82 mM DMSO. The instrument's built-in water peak suppression program was used during spectrum acquisition to reduce the influence of the water signal on the target peak and improve the product peak response. For quantitative calculations, all characteristic peaks of the liquid products were normalized to the DMSO peak at a chemical shift of 2.63 ppm.

[0078] Using the cathode electrode from Example 2 and Comparative Example 2 as the working electrode, a platinum mesh as the counter electrode, and Ag / Agcl as the reference electrode, an electrocatalytic carbon dioxide experiment was conducted at a series of potentials using a KHCO3 solution saturated with CO2 passed through for 20 min as the electrolyte and a completely airtight H-type cell as the electrolytic cell. The gas phase and liquid phase products were measured by gas phase and NMR.

[0079] Example 5

[0080] Following the testing method in Example 4, a series of electrodes with different PTFE contents prepared in Comparative Example 3 were used as working electrodes, platinum mesh as counter electrodes, and Ag / Agcl as reference electrodes to conduct electrocatalytic CO2 reduction experiments.

[0081] The molecular catalysts synthesized in the examples were characterized and analyzed in catalytic experiments, and the results are shown below.

[0082] Figure 2 The SEM image of the CuCu-salophen@KB electrode shows that, apart from the relatively uniform distribution of carbon black on the carbon fiber surface, no CuCu-salophen aggregation was observed. The EDX elemental distribution map indicates that Cu, N, and C elements are uniformly distributed along the direction of the carbon black on the carbon paper surface, and the signal intensities of each element are consistent. These results demonstrate the successful loading of CuCu-salophen@KB onto carbon paper.

[0083] Figure 3 TEM images of the CuCu-salophen@KB material show the carbon capsule structure of carbon black, and no aggregation of CuCu-salophen was observed.

[0084] Figure 4 A comparison of the Cu 2p high-resolution X-ray photoelectron spectra of CuCu-salophen@KB and CuCu-salophen powder in (a) revealed that, compared to CuCu-salophen, the characteristic peaks of Cu 2p1 / 2 and 2p3 / 2 in CuCu-salophen@KB shifted towards higher binding energies, indicating that Cu in the catalyst CuCu-salophen... 2+ The chemical environment changed, which further supports the π-π stacking interaction between uCu-salophen and carbon black. (b) In the figure, the XPS of Cu 2p of CuCu-salophen@KB shows two distinct peaks at 934.5 eV and 954.3 eV, which are attributed to the 2p1 / 2 and 2p3 / 2 energy levels of Cu, respectively. In addition, satellite peaks at 940 eV and 965 eV also appear in the spectrum, which indicates that the chemical state of Cu in this electrode is mainly divalent copper (Cu). 2+ (c) In the figure, the XPS plot of C 1s shows that the peak at 284.7 eV is mainly attributed to the binding energy of C=C or C-C bonds in the benzene ring, indicating that the electrode surface contains an aromatic carbon structure. The peak with a binding energy of 285.8 eV can be attributed to the CN group, while the peak at 288 eV is likely the peak belonging to the C=O double bond. From the above information, it can be seen that CuCu-salophen@KB was successfully prepared.

[0085] Figure 5 The cyclic voltammetry curve of the Cu-Cu-salophen homogeneous system (a) shows a pair of reversible redox peaks: the oxidation peak is located at 0.57 V (vs. RHE), and the reduction peak is located at 0.51 V (vs. RHE). This is attributed to the Cu in the Cu-Cu-salophen system. 2+ / + The redox properties were examined. No new redox couples appeared in the cyclic voltammetric curves of the heterogeneous and homogeneous systems before and after electrolysis; only the positions of the redox couples deviated. This result preliminarily indicates that a certain degree of stability was maintained during electrolysis.

[0086] Figure 6 The diagram shown in (ad) illustrates the molecular structures of CuCu-salophen, CuCu-salophen-ph, CuCu-salophen-ph-NO2, and CuCu-salophen-Br.

[0087] Figure 7 (a) The linear voltammetry curve shows that the carbon dioxide reduction potential of the CuCu-salophen@KB electrode shifted positively by 250 mV relative to the onset potential of the Cu-salophen@KB electrode. Furthermore, the current of the CuCu-salophen@KB electrode was higher than that of the Cu-salophen@KB electrode throughout the applied potential range. (b) The gas phase product diagram shows that the main hydrocarbon reduction product of the Cu-salophen@KB electrode is CH4, while the main hydrocarbon reduction product of the CuCu-salophen@KB electrode is C2H4. This result, to some extent, indicates that CuCu-salophen has the advantage of CC coupling over Cu-salophen.

[0088] Figure 8 The LSV curves of the CuCu-salophen@KB working electrode with different PTFE contents show that, at the same potential, the current of the CuCu-salophen@KB electrode decreases with increasing PTFE content. The product distribution diagram indicates that the CuCu-salophen@KB electrode achieves the best carbon dioxide reduction effect when the PTFE content is 40%.

[0089] Figure 9During electrolysis at a constant potential using the CuCu-salophen-Ph@KB electrode, the current density increases with increasing electrolysis voltage. As shown in product results (b), at lower potentials, the main products catalyzed by the catalyst are H2 and CO. With increasing voltage, the Faradaic efficiency of C2H4 begins to increase rapidly when the voltage reaches approximately -1.0V, reaching a maximum at -1.4V. At FE(C2H4) = 32.44, the Faradaic efficiency of hydrocarbon products at this potential exceeds 40%.

[0090] Figure 10 Electrochemical impedance spectroscopy (EIS) measurements and the fitted circuit diagram were performed. In the EIS spectrum, the semi-circular diameter of the bimetallic CuCu-salophen@KB working electrode was significantly smaller than that of the monometallic Cu-salophen@KB working electrode. The results indicate that the bimetallic CuCu-salophen@KB-loaded electrode exhibits the smallest charge transfer resistance.

[0091] Table 1. Faraday efficiency of CH4 and C2H4 at different potentials under CO2 atmosphere for CuCu-salophen, CuCu-salophen-NO2, CuCu-salophen-Br, and CuCu-salophen-Ph.

[0092]

[0093] Table 1 lists the Faradaic efficiencies of CuCusalophen@KB, CuCusalophen-Br@KB, CuCusalophen-NO2@KB, and CuCusalophen-Ph@KB in the CO2 reduction process to generate C2H4 and CH4. The results show that when electron-withdrawing groups are substituted in CuCusalophen, the Faradaic efficiencies for both C2H4 and CH4 decrease to some extent. Increasing the conjugation and electron-donating groups in the CuCusalophen molecule, in the preparation of CuCusalophen-Ph@KB, improves the Faradaic efficiencies for both C2H4 and CH4.

[0094] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a binuclear copper-based molecular catalyst, characterized in that, Includes the following steps: (1) Under stirring conditions, o-phenylenediamine solution was added dropwise to 2-hydroxy-5-methylisophthalaldehyde solution, and the reaction was refluxed under an inert atmosphere to obtain cyclic salophen ligand; The molar ratio of 2-hydroxy-5-methylisophthalaldehyde to o-phenylenediamine is 1:1, and both the o-phenylenediamine solution and the 2-hydroxy-5-methylisophthalaldehyde solution are anhydrous methanol solutions. (2) The salophen ligand was dissolved in DMF at room temperature, and then copper acetate was added. The reaction was carried out under an inert atmosphere and the solid was collected by vacuum filtration to obtain the binuclear copper-based molecular catalyst CuCu-salophen. The molar ratio of the salophen ligand to copper acetate is 1:2 to 1:

6.

2. A binuclear copper-based molecular catalyst, characterized in that: The catalyst was prepared using the method described in claim 1.

3. A method for preparing a copper-based bimolecular-carbon-based heterogeneous catalyst, characterized in that: The catalyst described in claim 2 is mixed with conductive carbon black at a mass ratio of 1:6 to 6:1; the mixture of catalyst and conductive carbon black is dispersed by ultrasonication; stirred, centrifuged, washed, and dried to obtain a heterogeneous catalyst.

4. A copper-based bimolecular-carbon-based heterogeneous catalyst, characterized in that: The heterogeneous catalyst was prepared using the preparation method described in claim 3.

5. The application of the copper-based bimolecular-carbon-based heterogeneous catalyst according to claim 4, characterized in that: The heterogeneous catalyst is used for electrocatalytic carbon dioxide reduction.

6. A method for preparing an electrocatalytic carbon dioxide reduction cathode, characterized in that: The heterogeneous material in claim 4 is well dispersed, the dispersion is sprayed onto carbon paper fiber, and dried to obtain a cathode of heterogeneous catalyst.

7. An electrocatalytic carbon dioxide reduction cathode, characterized in that: The cathode is prepared using the method described in claim 6.

8. The application of the electrocatalytic carbon dioxide reduction cathode according to claim 7, characterized in that: The cathode is used for electrocatalytic carbon dioxide reduction.

9. The application according to claim 8, characterized in that: Using the cathode as the working electrode, a platinum mesh as the counter electrode, an Ag / AgCl electrode as the reference electrode, and an aqueous solution of KHCO3 as the electrolyte, an H cell is used as the electrolytic cell. After CO2 is introduced into the KHCO3 solution, constant potential electrolysis is performed.

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